Iran says it's scaling down plutonium production plans at the country's only, partially built heavy-water reactor, an announcement seen as a gesture toward next week's negotiations with world powers over the Islamic Republic's controversial nuclear program.

According to the announcement, the reactor at Arak in central Iran will be redesigned to make less waste plutonium than what is required for the core of a nuclear weapon.

"The amount of production of plutonium in Arak ... will be less than one kilogram," Salehi said. "We are redesigning the reactor."

Iran's Supreme Leader Ayatollah Ali Khamenei says it is 'stupid, idiotic' to expect country to limit its missile program. (Office of the Supreme Leader/ Associated Press)

The change of plans is part of a deal that Iran is negotiating with world powers to ensure that its nuclear program will not produce an atomic weapon, in exchange for the lifting of international sanctions.

Salehi's remarks were the first indication of production plans, although he indicated during negotiations in April that plutonium production could be limited.

Since striking an interim deal in November, Iran and the six world powers — the five permanent UN Security Council members and Germany — have held several rounds of talks to try hammer out a final deal.

Under the November agreement, Tehran stopped enrichment of uranium to 20 per cent — which is a possible pathway to nuclear arms — in exchange for the easing of some Western sanctions.